Web Exclusive: Digital Press Speed Limits

Do you believe every spec you read online or in print? When it comes to digital output, manufacturers commit in writing that their production printers and presses can run at maximum rated speeds from 60 to 120 color, letter-size pages per minute (ppm). These numbers, however, beg for some critical thinking: What exactly do OEMs such as Canon, HP, Kodak, Konica Minolta, Ricoh, and Xerox mean by the term full rated speed? And, when an operator reads a machine description that specifies a rated speed, what does that actually tell him or her?

Production speed ratings are best-case scenario performance numbers tallied in optimal, lab-like conditions. To be taken with a grain of salt, these readings are not taken in real-world print shop environments in which different paper may need to be loaded, color is calibrated, operator skills vary, and maintenance needs to be performed over the course of several shifts or even several days. So, what is required to consistently operate a digital press as close to rated speed as possible?

“It’s not so much the optimal, ‘clean- room’ conditions,” says Mike Fego, Konica Minolta product manager for Production Print. “It’s more the paper size and weight” that can limit digital printer and press speeds more than just about any other variable.

It depends, too, on the types of print applications you’re running, of course. “An MFP [multi-function printer] with an embedded RIP, printing a variable data job, isn’t going to be able to run at full rated speed,” explains industry analyst Jim Hamilton, group director at market research firm InfoTrends, where he oversees production consulting services, including production copying and digital printing. But many higher-end devices in the printer-only category, he adds, “claim that they can print at rated speed on all stocks. In a lot of people’s minds, that [ability] is what defines a ‘digital press.’”

Hamilton noted that many MFPs still experience engine slowdowns when they run heavier stocks; some go up to 300 gsm, others to 350 gsm. “Even the next tier of products has this problem,” he says, citing the Xerox DocuColor 8000 line of production printers/copiers as an example. “But now Xerox has a version of the 700 that’s much better;” featuring different speeds for different media. Of the 700’s performance, one printer confirmed, “I run the heck out of it—all sorts of stocks—and rarely does it give me any trouble.”

Konica Minolta’s bizhub Press C8000, some 80 percent of which are being placed in commercial print shops, is one of several OEM models now employing a second fusing station to expedite speed on heavier stocks. Fego explains the underlying science: “In an electrostatic printer with a single fuser unit, the paper has to slow down after the image is on the page, as it goes through the oven.”

Lending its engineering perspective, Xerox added that its xerographic (electrophotographic) dry photocopying technique has a constant speed. “At whatever velocity a given print engine runs, we feed it [paper] at that rate,” says David Mueller, system engineering manager at Xerox.

For Kodak, the NexPress SE 300 runs at its full rated speed—100 A4 four- or five-color ppm—for more than 600 substrates. High-capacity feeders and delivery units, inline solutions, and finishing modules enable even greater uninterrupted printing.

In Hewlett-Packard’s case, the Indigo press can print on up to 18-point substrates without slowing down, largely due to the technology’s oil-based ElectroInk. (There is no oil drying/fusing time required, as in the toner-based electrophotographic (EP) process.)

Many digital devices struggle with coated stock, too. As Hamilton warns, “The more shiny and glossy the paper is, the more of a problem it can pose.”

70% Utilization

How real-world are full rated speeds? Minus about 30 percent, according to HP’s calculations, if you account for downtime. That’s what the digital press OEM tells serious shoppers when they get to the number-crunching stage. The HP Indigo 7500 press, for example, has a top rated speed of 60 ppm in color (4/4). However, HP manages the expectations of customers and hot prospects, cautioning them that they can expect performance somewhere “in the range of 65 percent to 75 percent of this utilization,” explains Rolando Martinez, North American category manager for the manufacturer’s high-end Series 3 presses. Instead of 60 ppm, “42 ppm is a more realistic number,” he acknowledges.

That said, Martinez also is quick to point out that some HP customers have utilization percentages at 80 percent and more. “There are just so many production factors to consider,” he says, and the fewer the variables, the faster the run. Martinez cited photobook customers who can run at 54 ppm (90 percent utilization) because there are no paper changes. Plus, he added, “a very experienced operator can achieve a much higher utilization.”

But don’t look for HP’s real-world ppm “utilization” numbers to be published in any marketing materials. You won’t find them there—not because rated press speed statistics are propaganda, but “because they vary too much,” Martinez says. “There would be too many footnotes.”

Secondly, these page-per-minute stats are based on A4 paper sizes. As Kevin Horey, VP of production products in Xerox’s Graphic Communications business group, put it, “Not many of our commercial print customers run an 8.5x11 [inch] piece of paper through [our digital presses].” David Mueller, Horey’s colleague, adds that 11x17 and 12x18-inch sheets, even those 19 inches wide, are more commonplace in production print environments. Fego, their competition at Konica Minolta, notes that “those 13x19 sheets are in the transport longer and the toner is working harder.”

RIPing through Data

Once you've optimized the system’s hardware, what’s the next step? The digital front ends (DFEs) or RIPs that drive digital presses must process data quickly enough to drive presses at their full rated speeds, Global Graphics CTO Martin Bailey told an audience at the IMI Digital Printing Presses conference last June. And it’s not only about speed, either. “The challenge isn’t just to be fast enough,” Bailey says. “The real challenge is to achieve that goal without incurring an uneconomically high cost for the bill of materials to build the DFE.”

Press manufacturers want to minimize the costs of the DFE compared with the cost of the press, he points out. Yet they have to ensure their products help print shops respond to market opportunities such as the growing market for photobook printing and personalized direct marketing materials. Bailey went on to discuss his firm’s approach to working with HP on its SmartStream Production Pro Print Server and Ultra Print Server DFEs. Global Graphics is the developer of the Harlequin RIP that has been used to drive the HP Indigo digital press range for the past 10 years.

For graphic-intensive projects and direct mail with complex variable data print (VDP) elements, particularly, “the RIP has to keep up with the data flowing into it,” notes Konica Minolta’s Fego. When it comes to rated speeds, there’s an assumption that the RIP is powerful enough so that the digital press doesn’t have to wait for printable data. (Another basic assumption is that the device is warmed up and ready to go.)

HP analyzes files in advance in a lab, performing capacity tests per application; their RIPs are scalable. Like most vendors, Konica Minolta offers a variety of RIPs, from basic embedded ones to Creo front-end server styles and its own proprietary RIP solution, which has been on the market for about one year. It even offers EFI’s high-end Fiery QX100 server for “extreme” production printing.

“You may need a different profile for different printed products,” adds InfoTrends’ Hamilton, depending on media thickness and coatings. In the case of EP printers and presses, for example, if someone is producing internal book pages on 24-pound text and then switches to 110-pound cover stock, the fuser needs to heat up and/or cool down, adding time into the equation and decelerating performance ratings.

Indeed, Xerox’s “mixed media mode can change the temperature of the fuser and have a direct impact on productivity,” agrees Mueller. “It’s a function of heating and cooling the thermal mass inside the machine.” A slowdown is inevitable to maintain image quality and fix, he explains, because “larger gaps are required between the paper [path] to allow the fuser to adjust temperature when switching between heavy and lighter weight papers.”

In the case of high-speed inkjet web presses (see sidebar), such as HP’s T series and Kodak’s Prosper, the front ends are quite robust. Some printers even “are adding multiple blade servers” to these devices, notes Hamilton, for ultra-high processing power.

Start Fast, Finish Slow?

What other factors come into play when determining realistic speeds? There are back-end production concerns such as the dreaded bindery bottleneck. Inline finishing can slow down the process. “Most products are designed to match machine throughput,” Xerox’s Mueller notes, such as stackers. But, he adds, “other mechanical actions—like gluing, jogging, punching, and folding—take time and can lead to low production.”

Mueller cites the example of a dual stapled set producing a job requiring two-page sets with dual staples. “We’d have to skip a pitch [panel or frame] to compensate,” effectively cutting productivity by one third. “When selecting finishing actions, users should be aware it can significantly impact productivity,” the engineer stresses.

The “Really Smart People” at Xerox and its Palo Alto Research Center (PARC) have conducted a lot of impressive research over the years, but one thing they haven’t figured out (yet), jested Mueller, is how to alter the laws of physics.

While inline finishing can optimize labor and offer less user intervention, HP nonetheless typically recommends near-line finishing systems. “With inline, you’re only as strong [or fast] as your weakest link,” Martinez says. “Near-line makes [adding] redundant systems easier.” A finishing line independent of the press is ideal, he added, because if it goes down the press can keep printing. “It can also be shared across multiple printing devices.” An existing offset printer already may have an offline bindery, he added.

The bottom line for printers calculating pressroom productivity: Keep in mind that you can seldom rely on manufacturers’ speed ratings. OEMs “tend to be either overly cautious or overly optimistic in most cases,” warns Colorado-based dealer Star Graphic Supplies. “Certain presses…were rated at speeds much higher than they could ever actually run and produce salable work.”

The Different World of Inkjet Web Presses

The big inkjet web presses are a different print animal, obviously, whose rated speeds are measured in feet, not pages, per minute: up to 400 feet-per-minute (fpm) in both monochrome and color for the HP T300 with its 30-inch roll. Unlike their cut-sheet cousins, heavier stocks don’t pose such a challenge for inkjet webs, but heavier ink coverage does.

“There’s really no box slowdown because of paper weights,” notes Moisha Clark, HP’s North American category manager of the high-speed inkjet web press. “The real question with these presses is, what kind of density do I want to put down on the paper and how fast do I want to go?” The key is having the right number of dryers, Clark adds. Using the T300 as an example, speeds slow to 300 fpm when color is more critical and higher ink densities are required. Even with a 25 percent production reduction, that’s still churning out high multi-million-quantity monthly impressions at a fast rate of speed. And much like an offset press, “operators have the ability to dial it [speed] down, if they want, for slightly richer color.”

Even the financial model is different, explains Clark, who spent 17 years on the Indigo side. “Customers incur a click charge on the Indigo every time the cylinder goes around. But with the T200, T300, T350, and T400, it’s based on how much ink you are laying down.” Still, HP’s 70 percent utilization rule applies for its inkjet web ‘lab’ speeds, too, accounting for job change-overs, preventative maintenance, human factors, and other production variables. In the real print world, a rated speed of 400 fpm translates to approximately 280 fpm.

Here, also, “finishing is a huge conversation with customers,” Clark adds. “One size does not fit all. We can deliver at full speed, but can a said [finishing] manufacturer accept it? A lot can. We have great finishing partners.” But again, it depends on what kinds of jobs you’re running. “Can a dedicated finishing line adapt to different sized applications?” asks Clark. “Or is it one size frequently, such as books, and you’re running the doors off?” HP’s approach to finishing is highly consultative. “It’s not just about the box,” he emphasizes. “It’s the end-to-end solution.”

“There can be feeding problems with higher-coverage jobs, especially on the inkjet side,” adds InfoTrends’ Hamilton. “If there’s more water on a certain part of the page … [it adds] weightiness.”

Other speed factors should be considered with inkjet web presses, according to Clark. “How do you automate?” he concluds. “Are you using a straight roll-to-roll configuration, or will you use a Zero-Speed Splicer [from Megtec]? We offer turret rewinders that can make your operation more efficient, too.”